Introduction to the CohortBetween 1994 and 1996, the Adult Changes in Thought (ACT) study enrolled 2,581 cognitively intact adults, aged 65 and older and members of the Group Health Cooperative (GHC) health care system in the Seattle area, Washington, USA. Investigators enrolled an additional 811 individuals from 2000-2002, for a total of 3,392 participants. Since enrollment, participants have undergone evaluations every two years. The purpose of the ACT study is to prospectively examine the incidence of AD and dementia, as well as risk factors for those conditions. At enrollment, 23% of the original cohort members (those enrolled from 1994-1996) were aged 65-69, 30% were 70-74, 24% were 75-79, 15% were 80-84, and 7% were 85 or older. Fifty-nine percent were female. The population from which the cohort members were sampled was middle class.

Ethnicity BreakdownNearly all original cohort members (91%) were white, 4% were African-American, and the remaining were of other or unspecified origin.